The present disclosure relates, in various exemplary embodiments to certain hole transport polymers and their synthesis. The hole transport polymers have improved anti-deletion, charge mobility and mechanical properties that can be used in an overcoat composition for long life photoreceptors.
In the art of electrophotography, an electrophotographic imaging member or plate comprising a photoconductive insulating layer on a conductive layer is imaged by first uniformly electrostatically charging the surface of the photoconductive insulating layer. The plate is then exposed to a pattern of activating electromagnetic radiation, for example light, which selectively dissipates the charge in the illuminated areas of the photoconductive insulating layer while leaving behind an electrostatic latent image in the non-illuminated areas. This electrostatic latent image may then be developed to form a visible image by depositing finely divided electroscopic toner particles, for example from a developer composition, on the surface of the photoconductive insulating layer. The resulting visible toner image can be transferred to a suitable receiving member such as paper. This imaging process may be repeated many times with reusable photosensitive members.
Electrophotographic imaging members are usually multilayered photoreceptors that comprise a substrate support, an electrically conductive layer, an optional hole blocking layer, an optional adhesive layer, a charge generating layer, a charge transport layer, and an optional protective or overcoating layer(s). The imaging members can take several forms, including flexible belts, rigid drums, etc. For most multilayered flexible photoreceptor belts, an anti-curl layer is usually employed on the back side of the substrate support, opposite to the side carrying the electrically active layers, to achieve the desired photoreceptor flatness.
One type of multi-layered photoreceptor that has been employed as a belt in electrophotographic imaging systems comprises a substrate, a conductive layer, a charge blocking layer, a charge generating (photogenerating) layer, and a charge transport layer. The charge transport layer often comprises an activating small molecule dispersed or dissolved in a polymeric film forming binder. Generally, the polymeric film forming binder in the transport layer is electrically inactive by itself and becomes electrically active when it contains the activating molecule. The expression “electrically active” means that the material is capable of supporting the injection of photogenerated charge carriers from the material in the charge generating layer and is capable of allowing the transport of these charge carriers through the electrically active layer in order to discharge a surface charge on the active layer. The multi-layered type of photoreceptor may also comprise additional layers such as an anti-curl backing layer, required when layers possess different coefficient of thermal expansion values, an adhesive layer, and an overcoating layer. Commercial high quality photoreceptors have been produced which utilize an anti-curl coating.
Imaging members are generally exposed to repetitive electrophotographic cycling which subjects exposed layers of imaging devices to abrasion, chemical attack, heat and multiple exposure to light. This repetitive cycling leads to a gradual deterioration in the mechanical and electrical characteristics of the exposed layers. For example, repetitive cycling has adverse effects on exposed portions of the imaging member. Attempts have been made to overcome these problems. However, the solution of one problem often leads to additional problems.
Cracks developed in the charge transport layer during cycling are a frequent phenomenon and most problematic because they can manifest themselves as print-out defects which adversely affect copy quality. Charge transport layer cracking has a serious impact on the versatility of a photoreceptor and reduces its practical value for automatic electrophotographic copiers, duplicators and printers.
Another problem encountered with electrophotographic imaging members is corona species induced deletion in print due to oxidation of the charge transport molecules by chemical reaction with corona species. During electrophotographic charging, corona species are generated. Corona species include, for example ozone, nitrogen oxides, acids and the like.
Other problems affecting the performance of the imaging member include lateral charge migration and stress cracking in the photoreceptor. The concentration of charge transport molecules in the charge transport layer is a known factor affecting the degree of lateral charge migration. In particular, higher concentrations of charge transport molecules near the surface of the charge transport layer tend to result in a higher degree of lateral charge migration and more stress cracks.
In electrophotographic photoreceptor devices having a hole transport layer, the layer usually comprises hole transport triarylamine small molecules dispersed in polymeric binders. Because these small molecules are prone to crystallization in machine operating conditions, this crystallization induced phase separation of the hole transport layer could easily lead to the failure of the whole device. Accordingly, it is advantageous to maintain the hole transport layer amorphous. Appropriate selection and synthesis of polymer hole transport material is one method available to solve this problem. But, the synthesis of hole transport polymers normally requires proper catalysts and produces non-volatile side products. The purification of these catalyst and side-products is often very difficult. To date, few polymer hole transport materials have been successfully used in photoreceptor products. Accordingly, there is a need to identify hole transport polymers that promote future long life photoreceptor devices, and methods for the preparation of such hole transport polymers.